Various types of feed mechanisms exist in the machine tool industry to automate the loading and/or unloading of workpieces into and out of a turning machine. Turning machines such as conventional hollow-spindle lathes may include a motor-driven rotating spindle which has a collet chuck mechanism connected to one end thereof for gripping material to be machined. In initial workpiece machining, which may be termed primary machining operations, workpieces may be machined from raw bar stock that extends from within the spindle and is gripped by the collet mechanism. After the primary machining is completed, the machined workpiece may be cut from the bar stock. Thereafter, the collet mechanism may be opened and additional bar stock may be fed through the spindle so that a new portion of the stock material may be received in the collet chuck mechanism for machining. This cycle is repeated to form several machined workpieces from the bar stock supplied through the spindle.
In many instances, secondary machining operations may be performed on workpieces that have previously been machined using the primary machining operation described above. These secondary operations are required, for example, when a different tool is needed to perform additional machining. In such cases, the previously-machined workpieces may be individually placed in the collet mechanism for further machining. In these secondary machining operations, the machined workpiece is held by the collet mechanism. Once the desired machining is completed on the workpiece, the machined workpiece must be ejected from the collet mechanism.
In other applications, multi-spindle lathes may be used to manufacture a machined part. Primary machining operations may be performed on bar stock material extending from a first spindle, whereafter the workpiece may be transferred to a second spindle for secondary machining operations. Generally, bar stock material will not be located in the second spindle, and finished workpieces may therefore be ejected through the second spindle.
Various workpiece ejectors have been proposed for use in turning machines, such as conventional lathes used in secondary operations. Conventional workpiece ejectors may generally include an elongated ejector push rod that extends through the spindle of an otherwise conventional lathe. The ejector push rod may be attached to an external plate that is driven by fixed, external air actuators to move the push rod into engagement with a workpiece and thereby eject the workpiece from the collet mechanism. As a result of the inclusion of external actuators, the space required for installation of a lathe including such an ejector may be substantially greater. In addition, conventional ejectors of this type may be costly and complex.
Other workpiece ejectors, such as the type disclosed in U.S. Pat. No. 5,715,735, are located inside the spindle, occupying some of the space which would otherwise be available for workpieces, and thereby limiting the size of the workpiece that can be machined. An additional drawback of this type of spindle-contained ejector is that it may deposit the finished workpiece in an area generally in front of the chuck, on one of the lathe surfaces, such as a chip pan or the lathe bed. Once this limited area fills up, manual intervention may be required in order for the accumulated finished workpieces to be removed.
Still other workpiece ejectors may be designed such that the ejecting mechanism, such as a spring or a pneumatically actuated piston or drive rod, will be restrained by the closed chuck holding the workpiece. When the chuck begins to open, and before if has fully released the workpiece, the spring or pneumatic device will begin the ejection, thereby potentially damaging the surfaces of the workpiece, due to contact with the chuck jaws during ejection. Such movement of the workpiece before the chuck has fully released the workpiece may not be suitable when a fine surface finish is desired.
Improvements to unloading devices for turning machines are therefore desirable.